This invention is related to a method of and apparatus for analysis of cement and more particularly, analysis of cement used to secure pipe string in a wellbore drilled into the earth, with a pulsed nuclear magnetic resonance spectrometer.
In utilizing cement for construction purposes, there is a need to be able to determine both the extent of setting and strength of the cement once the cement has begun to set. A knowledge of the extent of setting allows one to determine how much time is available to transport and place the cement, thereby preventing the cement from setting in the cement transport and/or cement placing means. A knowledge of the cement strength as it sets, enables one to determine when the cement has enough strength to either support and/or secure other objects or to support itself.
In the drilling of wellbores for the production of hydrocarbons from subterranean strata, cement is pumped into the annulus between the pipe string run into the wellbore and the wall of the wellbore to both secure the pipe string in the wellbore and to prevent communication between different subsurface strata from occurring in the annulus between the pipe string and the wall of the wellbore. In placing this cement in the annulus, it is common practice to pump a volume of cement slurry sufficient to fill this annulus down the pipe string and then to displace this volume of cement slurry from the pipe string into the annulus, by pumping a displacing fluid, such as drilling mud, behind the cement slurry. It is important in conducting this operation to know the extent of setting of the cement used under wellbore conditions, in order to ensure that there is sufficient time to place the cement in the annulus between the pipe string and the wellbore wall, thereby preventing the cement from setting in the pipe string. Further, it is important to know the strength of the cement as it sets in the annulus between the pipe string and the wellbore wall, so as to be able to determine when the cement has enough strength to support and secure the pipe string in the wellbore.
Accordingly, there is a need for a method of and apparatus for analysis of cement and, more particularly, analysis of cement used to secure pipe string in a wellbore drilled into the earth, to determine both the extent of setting of the cement and the strength of the cement as it sets.